Mattresses typically use springs, such as helical coil springs made of metal, to provide support for the body, and to provide a degree of alignment for the spine and a springy and comfortable feel for the user of the mattress. Helical coil springs or compression springs absorb the weight of a person and provide support, including support for the hips, spine and shoulders.
Designs and methods for producing a mattress having embedded springs are well known. See, for example, U.S. Pat. No. 4,154,786 (Plasse). Pocket spring technology in which springs are separated from one another by a material, such as a fabric material, are also known see, for example, U.S. Patent Application Publication No. 2004/0025257 (Ahlqvist) and U.S. Patent Application Publication No. 2005/0257323 (Edling). The contents of U.S. Pat. No. 4,154,786 and of U.S. Patent Application Publication Nos. 2004/0025257 and 2005/0257323 are incorporated in full by reference herein.
People are concerned with electric and magnetic fields induced by steel or other metal coils inside a mattress, especially since they spend a third or more of their lives on or near the mattress. Some studies have shown the deleterious effects for blood circulation, and other adverse physiological effects, caused by such electrostatic noise induced in or by metal coils. The effects of such fields and noise on human health and brain functioning are not fully understood at the present time.
There is thus a need for alternative types of mattresses that use more organic material-based compression coils. In addition, wooden coil springs may have a longer useful life, and may reduce or eliminate audible noises from the mattress.
Rattan, reed and other types of cane have been used to provide support and comfort for a person lying or sitting. For example, U.S. Pat. No. 5,596,777 (Polus), the content of which is incorporated in full by reference herein, describes such a solution. However, rattan springs typically require a stabilizing or hardening frame.
Compression springs made of compressed wood are known. For example, EP 2002759 (Czel), filed Jun. 15, 2007, the content of which is incorporated in full by reference herein, describes an energy storing compression spring made of compressed wood.
Wood can be compressed before it is bent. This is usually done on a wood pressing or compressing machine, and the wood is typically left in the machine for many hours. If the compressing is successful, the fibers of the wood have shifted in position and the wood becomes flexible and bendable even in the cold state. This is sometimes known as cold bending.
An advantage of using non-compressed wood, however, is that it may require fewer processing steps or shorter processing time to produce the coils. Also, non-compressed wood processing allows for greater control of the size, including the length and cross-section, of the slat that is formed into the coil, and greater control over the orientation and position of the last turns of the coil, and thus greater control over the size of the end turns of the coil. In addition, compressing wood can change the internal wood fibers such that the wood becomes more difficult to shape and sand. Compressed wood can tear or rip more easily when it is chiseled or sanded, or chunks of the wood can thus become loose.
Compressed wood loses up to 20% or more of its original length. Since a piece of wood to be made into a coil must be knot-free, the presence of knots in the wood limits the maximum length of a piece of wood that is usable for making a coil. Therefore, the length of coil springs that can be made of compressed wood is shorter than it would be if the wood did not have to be compressed. In addition, wood compressing machines are expensive, the compression process takes many hours and consumes significant energy, and the lack of availability of compression machines in sufficient quantities limits the amount of wooden springs that can be produced. In addition, wood that is not freshly cut can become deformed during compression. Thus, wood to be compressed should be obtained early in the season, for example, by spring or by April. Such wood must be stored in a careful way after its compressed and must be used within a relatively short time, such as within 6-9 months after compression. Compressed wood that is stored for longer periods often does not stand up to the requirements for wooden springs or even for other uses, or may produce inferior quality products. Wood can store moisture between its grains or inside its plant cells. Wood that is stored for a prolonged period of time can tend to dry, which is a result of water leaving the cells. If the wood is left for a longer period, then continued drying of the wood will affects its mechanical properties, as the wood begins to shrink and to get harder. Once wood becomes dry after prolonged storage, its moisture cannot be reliably restored before compression. Compressing such wood can deform the wood in undesirable ways and such wood can yield an inferior product after compression.
A process of producing wooden springs from compressed wood also involves steaming or warming and then drying of the wood. In fact, in the case of the manufacture of wooden springs, repeated drying may be necessary. These very energy intensive steps are not necessarily required for the production of wooden springs from non-compressed wood. Thus, the same amount of raw material will yield a greater amount of product for non-compressed wood, a smaller carbon footprint may be achieved using non-compressed wood processing, and a less costly process involving reduced need for energy may be obtained for the production of wooden springs using non-compressed wood processing. Also, longer wooden springs may thus be obtained.
Compression of the wood results in a spring with greater spring bias or greater spring force. This is caused by the greater stresses in the wood caused by the compression. This compression, however, may create a greater, stronger spring that is capable of working harder longer. This spring force cannot be decreased beyond a certain minimum force for any given spring height. Thus, a softer, less firm feeling spring can be generated with coil spring made from non-compressed wood.
Non-compressed wood, since it requires fewer processing steps than wood that is subjected to heavy pressure and compression, may be described as a more “natural,” less processed wood product, and marketed as such.
It has been found, however, that non-compressed wood is also bendable if steamed, in a process sometimes known as the Thonet process. While the Thonet process is known, the following description provides, among other things, a new method for using non-compressed wood to make wooden spring coils.